[llvm] [SimplifyCFG] Treat umul + extract pattern as one cheap single instruction (PR #128021)

[Yingwei Zheng via llvm-commits]

================
@@ -0,0 +1,129 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
+target triple = "riscv64-unknown-unknown-elf"
+
+define i16 @basicScenario(i64 %x, i64 %y) {
+; CHECK-LABEL: @basicScenario(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp eq i64 [[Y:%.*]], 0
+; CHECK-NEXT:    [[MUL:%.*]] = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[Y]], i64 [[X:%.*]])
+; CHECK-NEXT:    [[MUL_OV:%.*]] = extractvalue { i64, i1 } [[MUL]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[CMP_NOT]], i1 false, i1 [[MUL_OV]]
+; CHECK-NEXT:    [[CONV:%.*]] = zext i1 [[TMP0]] to i16
+; CHECK-NEXT:    ret i16 [[CONV]]
+;
+entry:
+  %cmp.not = icmp eq i64 %y, 0
+  br i1 %cmp.not, label %land.end, label %land.rhs
+
+land.rhs:                                         ; preds = %entry
+  %mul = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 %y, i64 %x)
+  %mul.ov = extractvalue { i64, i1 } %mul, 1
+  br label %land.end
+
+land.end:                                         ; preds = %land.rhs, %entry
+  %0 = phi i1 [ false, %entry ], [ %mul.ov, %land.rhs ]
+  %conv = zext i1 %0 to i16
+  ret i16 %conv
+}
+
+define i16 @samePatternTwice(i64 %x, i64 %y) {
+; CHECK-LABEL: @samePatternTwice(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp eq i64 [[Y:%.*]], 0
+; CHECK-NEXT:    [[MUL:%.*]] = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[Y]], i64 [[X:%.*]])
+; CHECK-NEXT:    [[MUL_OV:%.*]] = extractvalue { i64, i1 } [[MUL]], 1
+; CHECK-NEXT:    [[MUL2:%.*]] = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[Y]], i64 [[X]])
+; CHECK-NEXT:    [[MUL_OV2:%.*]] = extractvalue { i64, i1 } [[MUL2]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[CMP_NOT]], i1 false, i1 [[MUL_OV]]
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[CMP_NOT]], i1 false, i1 [[MUL_OV2]]
+; CHECK-NEXT:    [[CONV:%.*]] = zext i1 [[TMP0]] to i16
+; CHECK-NEXT:    [[CONV2:%.*]] = zext i1 [[TMP1]] to i16
+; CHECK-NEXT:    [[TORET:%.*]] = add nsw i16 [[CONV]], [[CONV2]]
+; CHECK-NEXT:    ret i16 [[CONV]]
+;
+entry:
+  %cmp.not = icmp eq i64 %y, 0
+  br i1 %cmp.not, label %land.end, label %land.rhs
+
+land.rhs:                                         ; preds = %entry
+  %mul = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 %y, i64 %x)
+  %mul.ov = extractvalue { i64, i1 } %mul, 1
+  %mul2 = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 %y, i64 %x)
+  %mul.ov2 = extractvalue { i64, i1 } %mul2, 1
+  br label %land.end
+
+land.end:                                         ; preds = %land.rhs, %entry
+  %0 = phi i1 [ false, %entry ], [ %mul.ov, %land.rhs ]
----------------
dtcxzyw wrote:

Use named values.

https://github.com/llvm/llvm-project/pull/128021